The invention pertains to permanent magnetic work holders, and, more specifically, to magnetic work holders having release mechanisms to facilitate separation of the work holder from the workpiece.
Both permanent magnet and electromagnetic devices are commonly used in industry for handling ferromagnetic materials. In a typical installation, magnetic lifts are used to lift, or otherwise manipulate, workpieces of ferromagnetic material, such as steel. By way of example, a magnetic lift, secured to a hoist or robotic arm, is brought into contact with a workpiece, such as a steel sheet. So long as the magnetic attraction or holding power of the magnet exceeds the weight of the workpiece, the workpiece may be lifted, moved or otherwise manipulated so long as the magnet remains in contact with the surface of the workpiece. In this fashion, ferromagnetic metallic components may be conveniently transported between locations in the industrial environment, for example, without the need for otherwise gripping the workpiece or providing attach points on the workpiece.
This type of magnetic lift is very well known, and has been in industrial use for a long period of time. Typically, such lifts utilizing permanent magnets are comprised of a housing or body containing one or more permanent magnets. The body is provided with a lift point to which may be attached a hoist or similar device. One surface of the complete magnetic lifting assembly so described is designed to be complimentary in shape to the workpiece being lifted. In a wide variety of applications, the workpiece is relatively flat, meaning that the corresponding contacting face of the magnetic lift is also flat.
While this basic configuration is both convenient and effective, it presents certain significant problems when permanent magnets are the magnets of choice for the lift. Permanent magnets are capable of exerting substantial magnetic forces. In particular, modern rare earth-type magnets, such as neodymium, exhibit enormously powerful magnetic attraction when properly selected for size, number and alignment. Since the forces exerted by permanent magnet assemblies are constant, separating the magnetic lift from the workpiece after the workpiece has been manipulated or moved presents serious challenges.
Basically, in order to separate the magnetic lift from the workpiece, the workpiece must be held, in some fashion, while sufficient force is applied to the magnetic lift to cause it to part from the workpiece. In most applications, this separation is most easily accomplished by lifting one end or one side of the permanent magnet lift from the workpiece, thereby creating an air cap. Once a substantial portion of the contacting surface of the magnet has been separated from the workpiece, the magnetic attraction between the lift and the workpiece is sufficiently reduced to permit the magnetic lift to be completely withdrawn.
A number of methods have been devised for separating the magnetic lift from the workpiece. Smith, in U.S. Pat. No. 3,014,751, teaches the placement of a camming release handle in the center of the magnetic assembly. The camming element, pivotably connected to the handle, is brought into contact with the surface by rotation of the handle. Ross, in U.S. Pat. No. 3,319,989, teaches a similar technique, whereby the camming element and handle combination are mounted near one end of the magnetic lift body. Both of these techniques, however, result in substantial marring of the surface of the workpiece. The degree of marring is directly related to the hardness of the workpiece, camming element, and the force required to separate the lift from the workpiece. In addition, earlier designs exhibit substantial friction between the camming mechanism and the workpiece.
There is a need, accordingly, for an improved magnetic lift and associated release mechanism, which I describe herein.
The invention is a self-contained, portable, permanent magnet-type lift assembly which is provided with a non-marring, low friction release mechanism. The release mechanism is secured to one end of the magnetic lift assembly, and is in the general form of a rotatable cam/handle combination. The surface of the cam which contacts the workpiece is a pivoting roller provided with a non-marring surface. Disengagement of the lift from the workpiece is accomplished by bringing the roller cam into contact with the surface of the workpiece, and using the mechanical advantage provided by the cam handle to separate the lift from the workpiece. The cam is designed as a pivoting roller mounted on a bearing, permitting the cam roller surface to roll across the surface of the workpiece as pressure is applied to the operating handle, thereby reducing both friction and marring of the workpiece surface.